Small RNAs play remarkable roles in regulating gene expression by binding to Argonaute family proteins and guiding them to recognize their targets. A specific subfamily of Argonaute, named PIWI, binds PIWI-interacting RNA (piRNA) and promotes fertility in all animals tested to date. piRNAs and PIWI proteins are highly enriched in germ cells, and PIWI mutations lead to sterility and dramatically reduced germ-cell numbers. In addition, PIWI-like proteins are overexpressed in several cancer tissues and this overexpression has been linked to poor prognosis. However, the biogenesis of piRNAs, as well as the mechanism by which piRNAs regulate germ cell and cancer cell, remain largely unknown. In this proposal I will use specific experiments to address three fundamental questions about piRNA pathways using nematode C. elegans as model organism: What is the molecular mechanism of piRNA-induced gene silencing? What are the genes regulated by piRNAs? Finally, what are the components involved in piRNA biogenesis and downstream silencing? The understanding of this evolutionally conserved pathway has potential to provide novel therapeutic approaches for treatment of infertility and certain cancers. PUBLIC HEALTH RELEVANCE: Small RNAs play remarkable roles in regulating gene expression by binding to Argonaute family of proteins and guiding them to recognize their targets1. A specific subfamily of Argonaute, named PIWI, binds small RNA (piRNA) and has been linked to functions in stem cell maintenance and tumorgenesis of various cancers2-4. Here we propose to apply molecular, genetic and biochemical approaches to understand the biogenesis and mechanism of PIWI / piRNAs-mediated gene regulation, which have the potential to provide novel therapeutic strategies for treatment of diseases such as infertility and certain cancers. Reference 1. Ghildiyal, M., and Zamore, P. D. (2009). Small silencing RNAs: an expanding universe. Nat. Rev. Genet 10, 94-108. 2. Thomson, T., and Lin, H. (2009). The biogenesis and function of PIWI proteins and piRNAs: progress and prospect. Annu. Rev. Cell Dev. Biol 25, 355-76. 3. Lee, J. H., Sch|tte, D., Wulf, G., F|zesi, L., Radzun, H. J., Schweyer, S., Engel, W., and Nayernia, K. (2006). Stem-cell protein Piwil2 is widely expressed in tumors and inhibits apoptosis through activation of Stat3/Bcl-XL pathway. Hum. Mol. Genet 15, 201-11. 4. Liu, J. J., Shen, R., Chen, L., Ye, Y., He, G., Hua, K., Jarjoura, D., Nakano, T., Ramesh, G. K., Shapiro, C. L., et al. (2010). Piwil2 is expressed in various stages of breast cancers and has the potential to be used as a novel biomarker. Int J Clin Exp Pathol 3, 328-37.